1. Field of the Invention
The present invention is directed to systems and methods for casting metal foam objects.
2. Description of the Prior Art
In the manufacture of products such as automobiles etc., there exists an increasing demand for components to be made from materials that have a high strength to weight ratio. In order to meet this demand, much emphasis has been placed on finding materials that are considerably low in weight yet high in strength for manufacturing such components. One such material that has been proposed is foamed metal.
A metal foam is generally created by generating a gas in a molten metal bath so as to form a molten metal foam. The foam is then extracted and cooled. Metal foam offers various advantages as a replacement to standard metal such as meeting the above mentioned high strength to weight ratio, high shock or impact absorbing qualities, and sound absorbing qualities. The prior art teaches various methods for producing metal foam such as in U.S. Pat. Nos. 5,221,324 and 5,622,542. The known methods of generating the gas mentioned above include, among others: (1) the use of a gas supply, which blows or injects the gas into the molten metal; (2) the use of gas generating, or foaming agents, which release gas when heated; and, (3) the use of impellers to draw the desired gas into the molten metal bath. It is also know in the art to provide the molten metal with a number of additives to assist the foam in maintaining the integrity of the formed cells.
Although the prior art provides various methods for producing metal foam slabs, which can be cut to desired dimensions, there is very little teaching of methods of forming the foam into three dimensional (3D) shapes of more complex geometries. U.S. Pat. No. 5,865,237 teaches one such method. In this reference, a metal powder and a gas evolving foaming agent are heated in a chamber to create a metal foam. While the foam is being generated, the molten mixture is forced into a mould cavity. The mixture is then allowed to continue to foam within the mould in order to ensure that the foam fills the entire volume of the cavity.
The process taught by this prior art method includes various disadvantages. Firstly, the process must be carried out in a batch manner. That is, the production of a single piece involves each of the steps of charging the chamber with the required powders, melting the powders, forcing the material into the mould, finally, completing the foaming process, cooling the mould and extracting the finished article. For this reason, the process taught in U.S. Pat. No. 5,865,237 is very time consuming. Further, the step of forcing the foaming material into a mould cavity would require a force to be applied against the foam cells. This force would inevitably result in damage to some of the cells and, therefore, reduce some of the advantage of the foam material. In addition, the patent requires the use of a piston to force the foaming material into the mould. Since the piston of the '237 patent, which is made of a metal, is maintained within the heated chamber at a temperature to maintain the molten metal in such state, it will be understood that the piston would have a tendency to seize due to damage caused by the heat. Further, the transfer of the foaming material must be done at a very specific time in the process in order to ensure that sufficient post-transfer foaming occurs. Finally, the method of forcing foaming material into the mould cavity taught by the '237 patent does not allow of precise metering of such material. As such, the size and density of the final products would not be consistent.
The present invention seeks to provide a metal foam casting system and process that mitigates at least some of the disadvantages of methods known in the art.